The ability to determine the presence of an analyte in a sample is of significant benefit. For example, many metals and metal ions, such as lead, mercury, cadmium, chromium, and arsenic, pose significant health risks when present in drinking water supplies. To prevent the contamination of drinking and other water supplies, it is common to test industrial waste-streams before their release to the water treatment plant. Biological fluids, such as blood and those originating from body tissues, also may be tested for a variety of analytes to determine if the body has been exposed to harmful agents or if a disease state exists. There is also a need to test for other toxins, for example detection of trace amounts of anthrax in a variety of samples has recently emerged.
While many analyses are performed in solution, some have been adapted to lateral flow devices. Lateral flow devices may provide multiple advantages over solution methods, such as the ability to provide the reagents in a dry or nearly dry state. Lateral flow devices also may provide the user with a simple “all in one” kit, which has a long shelf life. However, conventional lateral flow devices are typically limited to detecting specific biological analytes.
Commonly available lateral flow devices include pregnancy test kits, which test for the presence of the hCG hormone. The analysis chemistry of these devices relies on a dye labeled antibody that binds to the hCG hormone, which is then trapped by a second antibody in a visualization zone. A disadvantage of this method is the need to isolate and synthesize an antibody specific to the analyte. Another conventional calorimetric lateral flow device detects a DNA analyte by hybridization with gold nanoparticles functionalized with complementary DNA (Glynou, K., et al., Anal. Chem., 75, 4155-60 (2003)). A disadvantage of this method is that the analyte must be a bio-molecule capable of DNA hybridization.